Polarization; Electric Representation Of The Probe And Its Cable - Hach POLYMETRON 9125 Operator's Manual

Transmitter 9125 – Conductivity / resistivity measurement
6.

Polarization

Electric representation of the probe and its cable

In a conductivity measurement with a 2 electrode
probe the measurement current is transmitted via the
electrodes. The current is ensured by electrons in the
electrodes and by ionic migration in the solution
measured. An electron exchange process occurs
between the solution and the electrodes.
A significant example below :
2 H O=H
2
and
2 H O +2e
2
This reaction requires energy and causes a potential
difference which does not rely on conductivity.
This phenomenon is known as polarization and may
be represented by the scheme below :
V
Cable capacity
Cc
Polarization
Cp
Rp
electric equivalent of the conductivity probes
+ -
+ O + 4e
2
- -
= H +2 OH
2
Conductivity
Rx
Page 57